Fairchild’s tropical garden column

Beware the dangers of the string trimmer


Fairchild Tropical Botanic Garden

Tools make our jobs easier, and the ability to make and use tools can distinguish us from other animals. But what if we use a tool the wrong way and actually harm something we are trying to help? That is just what happens when we use string trimmers aggressively near the bases of our trees and shrubs.

String trimmers, sometimes called weed-whackers, are powerful little engines that propel a single or dual plastic string at high enough speeds to chop down whatever is in its path. This tool can be very helpful in cutting grass in places your larger mower just can’t reach, like around trees or next to the house.

The problem with the string trimmer is that it can damage tree trunks if it gets too close. It doesn’t matter who wields the string trimmer, — you, your significant other or the guy who cuts your lawn — we all fall into the trap of trying to get that last blade of grass. Then WHAP, WHAP, WHAP, and your tree has a gash in it where bark used to be.

You might think, “So what? The tree’s trunk is tough, so I don’t need to worry about any small cuts or nicks.” The fact is that the area getting damaged, the bark or phloem, is responsible for protecting the tree and for transporting energy made by leaves down to the roots. On the outside of the tree things go down, and on the inside, in the xylem, things go up. If you damage the bark, you damage its ability to transport vital energy to other parts of the plant, which can result in weak, disease-prone trees and even death.

How do we turn the string trimmer away from its reckless path of destruction? First, keep it far from the trunks of any plants, big or small.

Have a conversation with the person who cuts your lawn about avoiding trunks. Then put rings of mulch around each tree in the middle of your grass. The mulch will not only create a physical barrier between grass and trunk, it will also decompose and create nutrients for your tree, as well as help to suppress weeds.

Use mulch at a depth of about eight inches in the shape of a doughnut with the middle of the mulch ring much less in height so it doesn’t touch the trunk. Piling mulch up against the trunk of a tree can cause rot.

If you are not sure if your plants are being damaged by string trimmers, walk your yard and look at the bases of your trees. If you see any cuts or nicks, you know what the cause is and how damaging it can be. String trimmers can be great tools if used correctly and if your plants are properly protected by mulch beds or rings. So be careful and protect those plants!

Jeff Wasielewski is an outreach specialist at Fairchild, an expert in South Florida horticulture and a professor of horticulture at Miami Dade College. He can be reached at jeffw@fairchildgarden.org.

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